Why is understanding the richness of species in the ocean important?The human population on earth is rapidly increasing and we now seem to be facing the sixth major biological extinction event in the history of the globe. We depend on and benefit from the goods and services provided by the oceans and their biota and many of these goods and benefits will only continue to be provided if biodiversity is preserved. Hence a number of policy commitments have been made to halt or reduce the rate of marine biodiversity loss. Species richness is an important component of biodiversity and relatively easily observed. I consider it important to understand how changes in fish species richness may affect our future.

You mention these many hypotheses for why species richness declines from low to high altitudes. Could you outline one that is particularly interesting to you?The latitudinal decline in species richness is the most general and robust pattern of biological diversity on Earth. Nobody has yet with sufficient certainty identified a winner among the many hypothesis proposed, partly because many of the potential drivers will co-vary: a change in latitude is accompanied by changes in average temperature, seasonality, and input of solar energy. I guess that eventually a combination of biological productivity and how past environments have affected rates of dispersal, extinction, and generation of species will provide the answer, and this answer will be important for predicting how marine ecosystems will respond to climate change and how their response should be managed. I suspect that the glaciations and changes in sea level height that happened during the quarternary period​ may have had a strong impact on the distribution of fish species richness we see today, but other factors are also likely to have contributed.

Are there any notable places/ecosystems that are becoming more or less rich with species? Why? And what does it tell us?Yes, in the northern Atlantic we are seeing major changes in fish distributions, such as mackerel and bluefin tuna occurring near Greenland. In the North Sea the total number of small fish species recorded in research surveys has been increasing, perhaps linked to changes in climate or to a reduction in the abundance of fish predators, while many of the larger species of fish and elasmobranchs​ are rarer now than before, most likely due to fishing. In the eastern Mediterranean there has been a major increase in fish species richness due to the influx of new species from the Red Sea through the Suez Canal. Also, global warming has been predicted to allow exchange of fish species between the Atlantic and the Pacific at the end of this century. These observations and developments show that climate and human impacts are able to change fish species richness significantly. The consequences for the goods and services the oceans provide have so far been difficult to predict.

What first interested you and/or got you involved in studying marine species richness?The regular shape of fish species size distributions in the sea and Stephen Hubbell's book on the neutral theory of biodiversity and biogeography. In addition I noticed that little work was being done to identify the natural and human drivers of fish species richness, even though this was obviously of high political and ecological importance.

How exactly would you define a 'small-scale fishery'?Small-scale fisheries vary from place to place; thus it is difficult to provide one definition that works for all. Generally speaking, however, it refers to fisheries that are strongly anchored in local communities, often with traditional and cultural significance, and that support local economy and local food security. Fishing mostly takes place on shore, nearshore, or in coastal waters and involves men and women using smaller vessels with smaller engines and more labour intensive methods.

What is your personal experience with small-scale fisheries?I have worked in many small-scale fisheries around the world, but am most familiar with those in Thailand, Mexico, Malawi, and Canada. Small-scale fisheries are different in these places, with different management systems, but they face similar economic marginalization and sustainability challenges. Things are not always in a state of despair, however. In these places, one can always find great community-based and locally-driven initiatives that contribute to conservation and stewardship of fisheries resources and marine environment. It is these contributions that we need to highlight and promote, rather than treating small-scale fisheries as a problem (e.g., too many people chasing too few fish).

Are there issues that affect smaller fisheries more significantly than the larger ones? Small-scale fisheries depend heavily on resources, for livelihoods, food security, and wellbeing. They are therefore more vulnerable to global changes, whether related to the environment or the market. Some small-scale fishers live in disaster prone areas and are exposed to higher climate-related risks. Small-scale fisheries are also disadvantaged if they have to compete in global markets, for instance through eco-labeling and certification schemes. They are closely linked to local communities and contribute directly to the local economy. Changes happening in the globalized world make it difficult, however, for them to maintain their economic viability, and millions of them therefore live in poverty, especially in the south.

Your talk includes the phrase 'the most essential things are invisible to the eye' - could you give an example of an essential thing that is invisible to the eye in the marine world?Since Harden Jones' Fish Migration (1968), digital-age technologies have resulted in a period of unprecedented discoveries. But in rendering the hidden lives of fish ever more overt, we may have gotten ahead of ourselves in racing to the next discovery. There is now, more than ever, a critical need for creative thought on how to integrate new discoveries into more sophisticated fisheries and ecosystem assessment models. The phrase in my title is inspired by the fables of Hans Christian Andersen and A. de Saint-Exupéry, which challenge the obvious with what we can imagine in our mind's eye.

One remarkable new discovery is the capture of spawning Japanese eels in the Western Pacific Ocean. Similar endeavors to find spawning eels in the North Atlantic have eluded ICES scientists for over a century. For Japanese eel, two decades of research led Katsumi Tsukamoto and his team to the first capture of ripe adults and fertilized eggs in regions near Guam – a remarkable coupe resulting from exceptional teamwork, persistence, and integration of the best science that our digital age has to offer. Still, we can only imagine in our mind's eye how adult eels navigate from the rivers and lagoons of Japan to find each other within one of the world's largest marine ecosystems.

What role has the advancement in technology played in allowing us to map migrations?First and foremost digital age technologies have allowed fish to map their own migrations, sometimes proving us very wrong. For instance, electronically-tagged sturgeon were recently discovered spawning in the Chesapeake Bay, where I had 20 years earlier led a scientific consensus concluding that sturgeons were extirpated. We had completely missed these behemoths in one of the most intensively studied ecosystems in North America.

Historically, scientists have struggled to connect the dots between fish concentrations or tagged fish separated in space and time. Today, telemetry approaches permit daily and even sub-minute resolution in mapping individual tracks. Movements across large environmental gradients are tracked across entire lifetimes using otolith chemistry. Improvement in hydroacoustics has expanded the spatial and temporal ranges over which fish aggregations can be followed. More traditional methods such as catch records, surveys, and tag-recapture now afford extremely rich databases to map fish migrations. Finally, telecommunications has dramatically increased our capacity to map movements across large marine ecosystems, share data globally, and evaluate fish distributions and movements against dynamic seascapes.

Could you explain one example of a collective agency, why it is important, and what effect such behaviour has on a stock or population?Collective agency describes system operations that pertain to group behaviors and lead to emergent population outcomes, including migration. Schooling is a principal example, but emergent properties of schooling are rarely considered in the spatial behaviors of stocks. My interest in collective agency largely grew from ICES working groups on how schooling, learning, and path dependency influenced stock structure, collapse and recovery. But recognition of collective agency goes back further within ICES to Harden Jones, who recognized that stocks in changing environments relied on redundancy and oversampling in the form of straying and multiplicity of spawning grounds. Still, it remains our creative challenge to understand how this type of diversity preconditions stocks to adapt, irrupt, collapse, evacuate, and shift their distributions in response to fishing and ecosystem change.

What particularly got you interested in population and migration ecology in the first place?Enamored by the "blue revolution," I took an early career detour to study mariculture in Japan. I loved living in Japan and was challenged by the task of balancing artificial foodwebs, but grew bored peering at fish in transparent tanks. I think for many marine scientists, the fascination and creative impulse starts with wondering what's going on beneath the sea's oft opaque surface. For me, this led to the pursuit of indirect methods (e.g., otolith studies) to infer the unseen dynamics of marine populations.